The Monster Mash
by Winekita
Summary: One-Shot. "It was the best Halloween prank ever!" That was to be the writing on the Stoll brothers' graves. Happy Halloween, everyone!


**_Busy bee is busy. Sorry I haven't been posting, but you guys know how busy I've been lately.  
_**

 ** _That, and I've been working on a top secret X-Men/Pan mix story in honor of a picture I saw on DA by my favorite Logurt (I don't ship it but love the art for) artist. It's very secretive right now, and probably will go onto Archive of Our Own if I feel it's too slashy (not erotic, don't worry) for my usual readers._**

 ** _It's still Halloween here in Hawaii, so HAPPY HALLOWEEN!_**

 _ **I own nothing you recognize as canon.**_

* * *

 ** _*~The Monster Mash~*_**

 _A Heroes of Olympus Fanfiction  
_

 _"It was the best Halloween prank ever!"_

That was to be the writing on the Stoll brothers' graves.

It had begun in the beginning of October when Travis Stoll said, "You know what we should do? A Halloween prank!"

"Don't we do one every year?" Connor objected.

"No. Well, yes, but we should really go all-out this year! Seeing as how we kicked monster butt especially hard and all…" He had trailed off instantly. Then, he broke out into a huge grin. "I got it!"

He whispered to his brother a most devious and diabolical prank. Connor gasped, "Are you insane!? They would kill us!"

"We'd be in the same boat as them, though, so they wouldn't know who did it. And we'd just choose the perfect thing that naturally disappears. Y'know, as insurance they won't find us."

The more Travis talked up the prank, the more Connor began to get on board with it. After ten minutes, the brothers finally began their research.

Just because they were notorious thieves and pranksters did not mean they didn't know how to research. That step was essential to every prank. One had to observe their quarry, know their weaknesses, know every nook and cranny for hiding places at ground zero of the prank, map escape routes, and get a feel of the strength of the prank.

This research required the brothers to steal a few books from the Hecate cabin. It was easy, since they were out at the lake.

"Make sure you grab the ones I said," Travis told his brother as they rummaged through the bookshelves for specific spell books. "Ones with temporary spells and non-negative effects."

"What are you doing!?"

The brothers turned to see Lou Ellen, the current head counselor for the Hecate Cabin, standing in the doorway with her hands on her hips. She scowled. "What do you think you're doing—stealing spell books that aren't meant to be seen by the unworthy?"

"We figured we'd expand our knowledge of the magical world," Travis said smoothly.

Connor nodded. "Is there one in here that teaches us how to win a fight against Voldemort?"

Lou Ellen glared at them. "What are you really up to?"

The brothers shared a glance, communicating silently. Finally, Travis grinned. "How would _you_ like to be on the delivering side of a prank with us?"

She cocked an eyebrow and said, "Go on."

* * *

One week later, invitations suddenly arrived on everyone's beds (or, in Leo's case, next to his head on the worktable in Bunker Nine). They read:

 _To Whom It May Concern,_

 _You are hereby invited to the **MONSTER MASH** , a spooktacular Halloween party in the main clearing of the cabins. Celebrate the spookiest time of the year with chilling music, haunting games, and of course a monster costume contest. The only requirement is that you have to be dressed in your best monster gear. No human costumes. Only monsters—from any mythology, if you wish._

 _We hope to scare you out of your wits this Halloween, starting at sundown!_

 _—The Stoll Brothers, hosted by the Hecate Cabin_

Needless to say, everyone was excited. Yes, the Stolls were known for their pranks, but when it came to parties, they could throw a good one. The Dionysus Cabin was the only one that could throw the best in the world, but the Stolls could come close if they really tried.

So, everyone that was in camp, sans Chiron and Mr. D (as long as it was confined to the cabins area, they were unconcerned) decided they would attend this monster mash. They were told to arrive before sundown, and anyone not in the area when the sun set would be kept out—they'd have to enter their cabins through emergency back doors if they needed to get into their beds for the night.

So, it was before sunset when the Seven (for Frank and Hazel had been invited from New Rome) were hanging out in the clearing with the other campers. They conversed freely, drinking punch and joking around.

"Leo, how did you even manage to make that?" Hazel asked.

Leo flaunted his mecha-dragon suit by striking an action pose. He was covered from head-to-toe in bronze scales, his head encased in a bronze dragon head that moved and spat fire at the touch of a button in Leo's clawed gloves.

"I built a giant flying warship and a big dragon and you're wondering how I made a suit?" Leo challenged. "What about you?"

Hazel put her hands on her hips. Her arms were covered in feathers, and her boots had talons painted on them. "What do you mean?"

"What are you supposed to be?"

"I'm a harpy," she said. "I wanted to be one to honor Ella!"

Leo snorted. "What'd you do? Glue feathers onto your arms?"

"They're sleeves I bought at one of the stores in New Rome," she argued.

He turned to Frank. "And what are you? A basilisk?"

Frank frowned. "I'm a Qilin."

"You're chillin'?" Percy, in his Pegasus costume (as a dare from Blackjack), joked. "You look mad."

Frank huffed in annoyance. "A Qilin is a type of mythical creature in China." He gestured to his scaled-outfit topped with Chinese dragon horns on the hood. A tail had been sewn into the back of the jacket.

"Sometimes I think you make the Chinese stuff up," Leo complained.

"No, he's telling the truth," Annabeth said, fixing her sphynx costume. She went with an Egyptian sphynx, not Greek. "People today think the Qilin myth originated from when an emperor was given a giraffe as a present."

Leo yawned. "Wow. So, you're a Chinese giraffe, Frank? Creative."

Just then, a snarling werewolf head popped into Leo's view, two inches from his face. It howled murderously. Leo screamed and backed up quickly, toppling over Calypso in her fairy outfit (she argued that fairies could be vicious if they needed to be, which qualified as a monster).

Piper peeled off her werewolf mask and laughed. "Oh gods, Leo," she gasped. "You scream like a little girl!"

"I do not," he squeaked.

Calypso heaved her boyfriend off of her. "You scream like a girl, and you are as heavy as a hippo in that outrageous costume! You couldn't find lighter materials!?"

Leo scratched the back of his neck. "I was on a budget!"

Then, he caught sight of Jason and cocked his head. "Are you a flying monkey?"

Jason crouched low and gave an, "Ooh, ooh!" Then, he straightened, fixing his Wizard of Oz flying monkey costume. "Yeah. Piper wanted to be the Wicked Witch, but since it was monsters only, she went with a werewolf."

"'Cause werewolves are the bomb," Piper announced, putting her mask back on. "Way better than vampires!"

Leo scoffed. "C'mon! Vampires are so much better! At least they don't need a flea bath every month!"

"Werewolves don't solely depend on human blood," Piper defended. "They can eat any sort of prey, human or livestock."

"Sunshine," Leo whined. "You're on my side, right? Vampires rule, werewolves drool!"

Calypso shrugged. "Aren't vampires _emposai_? They most certainly are not ruling anything."

Leo put a bronze hand over his heart. "Not you, too, _mi sol_!"

"Attention, please!"

Everyone turned to the makeshift stage in front of the Hecate Cabin. The Stoll brothers, in matching Cheshire Cat outfits, tapped into their microphones and cleared their throats.

"Thanks for coming, everyone," Travis said.

"Before we start," Connor continued. "Did everyone put on their nametags?"

Before they were allowed to enter, the Stolls had required everyone to put on a _HELLO MY NAME IS_ tag on their person. It made no sense, since everyone knew everyone.

After a community nod, they continued. "Then, let us explain something."

"Whatever happens, please remember that it's only temporary," Connor said.

The crowd shifted. There was a prank—and someone was about to get it. But who?

"So, without further ado," Travis began.

"Welcome to the Monster Mash!"

A voice rose up in the air as dark fog curled around everyone's feet.

 _All within the party bounds,_

 _Shall be henceforth cursed while the sun is down._

 _Become the creature you so mimic,_

 _Be huge, monstrous, ghastly, or sick._

 _The curse enacted lasts only one night,_

 _So have your fun as a monster tonight!_

The fog rose up in a flash and covered everyone, including the Stolls on the stage. People screamed. Darkness was the only thing anyone could see for a moment.

And then, the fog was gone.

Hazel shook her head, which was pounding. Her nails felt harder and sharper than before. She looked at her arms. They were covered in golden feathers, but not in the cheaply-made way from before. There were no sleeves—the feathers were actually sticking out of her skin! Her feet were no longer covered in boots, but were actual bird feet! A tail of golden feathers now rested on her butt.

She shrieked. Her voice sounded much higher than it used to be, and much more shrill. "What is this!?"

Frank groaned next to her. He tried to clutch his head, but found it a little hard. His arms were shorter, and he was on all fours. He looked down; his hands were smaller, scalier, and green! He examined the rest of his body, which was shaped much like a horse's body, with a long, whip-like tail that ended in a plume. Spines lined his back, and it felt like there were horns on his head.

 _Why can't I transform back?_ Frank thought despairingly. "Guys, I think something's up with my powers…"

He looked around and blinked. Standing in a loose circle were a bunch of creatures. One was definitely a harpy-version of Hazel. The others…

Next to Harpy Hazel was a black Pegasus a little bit smaller than Blackjack, a human-sized sphynx with Annabeth's face, a tiny fairy, a werewolf in ripped girl's clothes, a flying monkey, and…holy Mars, that was a big dragon!

The Pegasus whinnied, "Uh…I don't think it's just you, dude."

"Percy?" Frank sputtered. "You—you're a horse!"

"Um, I don't mean to rain on your parade, but you are, too. At least, I think you are. You're that chillin' horse dragon thing, right?"

The Annabeth-faced sphynx said, "Yes, he's a Qilin. We've all been turned into a real version of our costumes!"

Jason scratched his head in a monkey-like way. "Really? Why?"

Frank looked to the stage, right as the Stolls—as matching Cheshire Cats—disappeared. Their smiles were the only things left behind for a split second, and then they were gone for good.

Piper howled in rage. "I'll kill those fooooooools!"

"Geeze, Pipes," boomed a deep voice. "You took not shaving your legs to the extreme!"

Everyone looked up to the bronze dragon towering over the group. Its brown eyes twinkled mischievously.

"Leo?" Percy asked nervously. "Is that you?"

"You bet! I'm so stoked!"

The fairy flying around the group landed on Leo's nose. "Are you serious? You're huge!"

"Is that Calypso?" Hazel squinted. "I can barely see her, and my eyesight is ten times better than usual right now."

Percy nodded. "She's glowing like Tinkerbell."

Leo's eyes lit up. "TinkerCalypso—no, Calypsobell! Awesome!"

The fairy flicked him in the eye, which made Leo rear up and rub his eye furiously. "You dummy! You're a _dragon_! Not even a drakon—a full blown _dragon_! Do you know what that can do to your mind?"

"I'll get a craving for sheep and start sleeping on piles of gold?" Leo guessed.

"Something like that, and you'll be way more aggressive. In fact, all of us becoming creatures is a bad thing! Human minds are fragile; change the outside and you slowly change the inside!"

Jason tried to stand up straighter than his monkey form would allow. Piper whined. Frank and Percy shifted on all four feet. Hazel's feathers fluffed out in alarm.

"What should we do?" Annabeth asked calmly, her tail curled around her feet.

The glowing ball of Calypso sat on Leo's large shoulder. "We need to find out who cursed us and why."

"Obviously the Stolls had a hand in it," Frank growled. "They disappeared before anyone could find the time to strangle them."

Annabeth looked thoughtful, putting a paw to her chin. "The invitation said the party was hosted by the Hecate Cabin. Are there any Hecate Cabin members in the crowd right now?"

They looked around. Percy spotted Clarisse instantly. As a challenge on her manliness—womanliness?—Percy had dared her to dress up as a unicorn to the monster mash. Her costume had been one of the My Little Pony: Friendship is Magic hoodies (Rarity being the unicorn she dressed up as). That was it. Now, though, she was a full-blown white unicorn with a lovely, flowing purple mane and tail and delicate features. Even the deadly horn looked beautiful on her.

That didn't mean she looked happy. No, she was downright furious, shaking her head like a bull at her boyfriend, Chris the Gremlin. She looked ready to stab anyone who got in her way.

One could still sort of tell who was who amongst the new monsters. For example, it didn't take a genius to figure out the one Cerberus in the crowd had once been Nico di Angelo, and the phoenix on his back was Will Solace (since those two never left each other for very long now). Katie Gardner was a willow tree dryad, tall and beautiful. Nyssa was an actual zombie, with brains peeking through her skull. Jake was see-through, meaning he was now a ghost.

"I don't see any of them," Leo announced. "No one here is from the Hecate Cabin."

"They must have all worked together to cast the spell," Annabeth mused. "We should be fine, then."

"Excuse me?" Calypso squeaked. "What about any of this is fine?"

Annabeth started to lounge, stretching out her new cat body on the ground. "The Hecate Cabin is known for casting spells that work with little nasty side effects. I'd be way more worried if it had been _just_ the Stolls casting the spell. If it had been just them, _then_ I'd worry for the state of our minds."

Everyone in the group relaxed. She had a point.

Piper growled, "I'm still gonna kill those two when this is over."

"Why?" Leo challenged. "Regretting your previous argument about werewolves being superior over vampires, flea queen?"

She nipped one of Leo's toes. "Shut up, fatso. I just don't like this situation being thrust upon me so suddenly. I'd still take werewolf over vampire any day."

"Fatso?" Leo grabbed his new dragon paunch, as dragons weren't known for being scrawny. "I'm not that fat, am I?"

"That's the price you pay for getting taller," Jason said with a monkey laugh.

"But Frank got taller and he didn't get fatter—he got buffer! Where's the fairness in that, I ask you!"

Hazel hopped up onto Frank's back. "Should we still be concerned?"

Annabeth shook her head. "I'm trying to remember exactly what the spell said, but I remember it said the curse would only last one night."

Calypso visibly relaxed. "If it's only one night, I'm perfectly fine with it. It takes a while for the mind to unravel, and though Leo's is impossibly small, one night isn't enough to change him."

"Hey!" Leo snorted smoke at his fairy girlfriend. She coughed and flicked glitter at him.

Percy stamped impatiently. "Y'know what? If we're stuck like this, in a real life version of Halloweentown II: Kalabar's Revenge, we might as well make the most of it! It's not like we're gonna hunt each other, right?" He flapped his wings and flew straight up. Then, he dove back down and landed on the stage.

"Hey!" he called, grabbing everyone's attention. "How many of you have seen a Pegasus boogie?"

He gestured to the DJ, a son of Dionysus who had been turned into a goblin. The goblin smiled and started up some music—Animals, by Maroon 5.

As soon as the music started, Percy the black Pegasus started hopping around in a horse dance. At first it was awkward, as he was testing out his new limbs, but then it became amazing. Some monster campers began dancing, forgetting the initial terror of becoming creatures. Others restarted their conversations.

The thing about demigods: they certainly know how to take things in stride. If the great Percy Jackson wasn't worried about being a Pegasus for a night, why should they be? Their lives weren't in danger if they stayed inside the party boundaries.

So, for the rest of the night, the camp for demigods became the camp for monsters. Everyone eventually got over the change and started bragging about how they were better than the creature next to them. There were a few strange side effects, like Leo (as the only large creature) eating the entire buffet or Clarisse shooting random bursts of magic every time she sneezed, but all-in-all, everyone had a ton of fun.

* * *

When the sun rose the next day, humans once again populated the party area—including two previously hidden Stoll brothers.

And within two seconds, those same brothers ran away as soon as they were spotted. Most of the campers gave up the chase, not really caring about the transformation prank since it did no harm.

However, Clarisse the ex-unicorn, Piper the ex-werewolf, and a few other rightfully mad campers were definitely determined to make this Halloween the last the Stolls would ever see.

Travis tried to defend them by calling back, "It was the best Halloween prank ever, though, you have to admit!"

That only made the campers more determined to send the brothers to their graves.

* * *

 ** _A/N: Happy Halloween, everyone! Hope you had a spooky time~! Sorry this came up at the last minute, but I literally spent all day on this, as I didn't have any time to work on it until today. Hope you enjoyed this short little piece!  
_**


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